1. Field of the Invention
The present invention generally relates to a bearing device to be mounted in various fluid systems, and more specifically to a bearing device for bearing a rolling element arranged in a fluid passage within a fluid system housing.
2. Description of the Related Art
A vehicle engine carburetor used as a fluid system is exemplified in FIG. 2. In FIG. 2, the carburetor includes a venturi 3 in the middle of an intake passage 2 within an intake pipe 1. A nozzle 4 which is connected to a fuel chamber (float chamber) is mounted on the narrowest portion of the venturi 3, and is made open so that fuel may be injected from the nozzle 4 by making use of a negative pressure generated in the venturi 3 to form a mixture gas. Typically, a throttle valve 5 for controlling amount of supplying the mixture gas to the engine side is disposed at the downstream side of the venturi 3 in such a manner that the valve 5 can be rotated by means of a bearing device 10 as will be described later.
The bearing device 10 is so structured as in shown in FIG. 3. A roller bearing 12 is fitted into a coupling bore 11 formed in a wall portion of the intake pipe 1 which faces the diameter direction thereof, and a shaft 6 of the throttle valve 5 is supported by this roller bearing 12. As the roller bearing 12 used herein, a general-purpose bearing having a plurality of balls 16 held between an outer race 13 and an inner race 14 by a retainer 15 is chosen. Since air flow must be shielded, the bearing used therefor is formed with seals such that sealing plates 17, 17 are arranged at the both sides. The movement of an acceleration pedal (not shown) which exerts on one end of the shaft 6 via a lever 7 allows the throttle valve 5 to appropriately rotate.
Due to the structural design of the above-stated carburetor, the throttle valve 5 may be assembled concurrently while the shaft 6 is passed to the roller bearing 12. Therefore, the coupling bore 11 in the intake pipe 1 may not be tightly engaged with the roller bearing 12, and the roller bearing 12 may not be tightly engaged with the shaft 6 of the throttle valve 5. This potentially results in clearance a or b at the respective engaged sections due to a dimensional error. If the clearance a or b is formed, air as well as impurities such as water, oil or grease permeates through the clearance a or b into the intake passage 2 since the rotation of engine may also generate a negative pressure in the intake passage 2. This causes the engine performance to be deteriorated. Therefore, a sealing measure against this malfunction has been desired. Further, this type of carburetor is disposed in an engine room having a large variance of temperature, resulting in a difference in thermal expansion among the following three essential components of the bearing device 10: the intake pipe 1, the roller bearing 12, and the shaft 6 of the throttle valve 5. Then, the same clearance a or b as above may be possibly formed at these engaged sections. In view of this, the above-described sealing measure has also been desired.
The carburetor typically includes a choke valve for controlling the amount of intake gas at the upstream side of the venturi 3. A bearing device for bearing this choke valve also requires the above-described sealing measure.
Some of the vehicle engine fuel systems may include a fuel injection system in place of a carburetor. A bearing device for bearing a throttle valve mounted in this type of fuel injection system also requires the same sealing measure.
Further, some fluid systems may include a fluid passage in which a higher pressure is generated than atmospheric pressure. A bearing device for bearing a rolling element disposed in such a fluid passage requires a sealing measure to prevent the fluid in the fluid passage from leaking to the outside therefrom.